Sequential injection methods, which are referred to below as SEFI methods (SEFI=Sequential Fuel Injection), are performed on internal combustion engines in which one injection valve is allocated to one cylinder or to one group of cylinders. A computer sets the values for the beginning and end of the activation of a respective injection valve depending on the particular operating condition of the internal combustion engine. A variant employed in practice consists in setting the injection start angle and calculating the end of injection from an injection duration. Another variant adopts the method of setting the injection end angle and calculating the injection start angle from a respective injection end angle and an associated injection duration.
A problem in both variants is the fact that it is not possible to exactly achieve the calculated angles for the start of injection and the end of injection. This is because in known SEFI methods for a 4 cylinder engine, a so-called segment signal is only emitted every 180.degree. of crankshaft angle. If an injection angle, whether a start angle or an end angle, is set at, for example, 552.degree. crankshaft angle, three segment marks are counted out after the beginning of the current work cycle, a crankshaft angle of 540.degree. thereby is reached. The missing 12.degree. are determined by counting out time pulses.
The number of time pulses which occurs within an angular range of 12.degree. crankshaft angle depends on the speed of the internal combustion engine. If there is a relatively rapid change in speed during the period of time between the calculation of the number of time pulses to be counted out and the instant at which the counting out of the pulses is actually started, the injection angle which is actually desired is missed by a considerable amount. Rapid speed changes within this period of time occur particularly in the starting period and in other cases in which the internal combustion engine initially has only a low speed, which is then increased a great extent.
The object on which the present invention is based is to provide a SEFI method which permits more exact achievement of predetermined injection angles than was hitherto possible.